Application of Enterococcus faecium KE82, an enterocin-A-B-P-producing strain, as an adjunct culture enhances inactivation of Listeria monocytogenes during traditional PDO Galotyri cheese processing.

The ability of the enterocin-A-B-P-producing Enterococcus faecium KE82 adjunct strain to inactivate Listeria monocytogenes during Galotyri PDO cheese processing was evaluated. Three artisan cheese trials from traditionally 'boiled' (85oC) ewe's milk were processed. The milk cooled at 42oC was divided in two parts: A1 was inoculated with Streptococcus thermophilus ST1 and Lactococcus lactis subsp. cremoris M78, and A2 with the basic starter ST1+M78 plus the KE82 adjunct (step 1). All milks were fermented at 20-22oC for 24 h (step 2); the curds were drained at 12oC for 72 h (step 3) and then salted with 1.5-1.8% salt to obtain the fresh Galotyri cheeses (step 4), which were ripened at 4oC for 30 days (step 5). Because an artificial listerial contamination in the dairy plant was prohibited, A1 and A2 cheese milk (200-mL) or curd (200-g) portions were taken after steps 1 to 5, inoculated (3-4 log CFU/mL or g) with L. monocytogenes no.10, incubated at 37, 22, 12, and 4oC for predefined periods, and analyzed microbiologically and for pH. L. monocytogenes declined without growth in all cheese curd portions contaminated after steps 2 to 5 (pH 4.36 to 4.84), when stored at 4 or 12oC for 15 days. The final net reductions of Listeria populations were by 2.00, 1.07, 0.54 and 0.61 log units higher in the A2 than A1 curd portions after steps 2, 3, 4 and 5, respectively. As regards step 1 conducted in simulation of the whole cheese milk fermentation process, L. monocytogenes declined by 1.47 log units more in the A2 than A1 milk portions after 72 h at 22oC; however, a slight (0.6-log) growth was preceded during the first 6 h at 37oC. In conclusion, E. faecium KE82 showed growth compatibility with the starter and enhanced inactivation of L. monocytogenes across Galotyri cheese processing. Combined acid-enterocin antilisterial effects were the weakest in the fermenting milks, turned to the strongest in the unsalted fermented curds, and reduced in the salted fresh cheeses.